Port C Pin Connections; Figure 3-8. Digital I/O Connections - National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual

Chapter 3
+5 V
LED
+5 V
Switch
In Figure 3-8, Port A is configured for digital output, and Ports B and C are configured for digital
input. Digital input applications include receiving TTL signals and sensing external device states
such as the switch in Figure 3-8. Digital output applications include sending TTL signals and
driving external devices such as the LED shown in Figure 3-8.

Port C Pin Connections

The signals assigned to Port C depend on the mode in which the 8255A is programmed. In
Mode 0, Port C is considered as two 4-bit I/O ports. In Modes 1 and 2, Port C is used for status
and handshaking signals with two or three I/O bits mixed in. The following table summarizes
the signal assignments of Port C for each programmable mode. See Appendix E, Register-Level
Programming, for programming information.
© National Instruments Corporation
TTL Signal
I/O Connector

Figure 3-8. Digital I/O Connections

14 PA0
22 PB0
30 PC0
13
DGND
Lab-PC+ Board
3-15
Signal Connections
Port A
PA<7..0>
Port B
PB<7..0>
Port C
PC<7..0>
Lab-PC+ User Manual